The role of hydrocarbon (hc) and nitrogen oxides (NO*) in photochemical smog formation was investigated. Samples of automobile exhaust with varying hc and NOz levels were irradiated in a smog chamber under conditions that resulted in levels of smog manifestations similar to those observed in the atmosphere, hc levels ranged from 0.3 to 5.0 ppmC, and NO* levels ranged from 0.08 to 1.4 ppm. Photooxidation of nitric oxide (NO) and formations of oxidant, peroxyacyl nitrate (pan), formaldehyde (HCHO), and nitrogen dioxide (N02) were used as smog manifestations. Results showed that except for the N02 yield, all smog manifestations were intensified by increasing hc; NOz inhibited the oxidant, pan, and

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This article deals with reactivity and photochemical modeling methods needed to develop emission control strategies for ambient ozone reduction, and with the uncertainties associated with relevant data and methods. Specifically, the article identifies and describes existing reactivity data for volatile organic compound (VOC) emissions from consumer and commercial products (CCF), and methods for developing control strategies for such emissions that take into account emissions reactivities. Existing reactivity data consist of Incremental Reactivity data and KOH-reactivity data. Both types of data are subject to uncertainties associated with • lack of experimental evidence, which is particularly severe for CCP emissions species; • theoretical derivation and/or experimental measurement of reactivity; and • variation of VOC reactivity with ambient conditions. Methods are described for using the reactivity concept to estimate the contribution of CCP emissions to ambient ozone. Also, to comply with one of the requirements of Section 183(e) of the 1990 Clean Air Act Amendments and with current U.S. Environmental Protection Agency policy on reactivity, existing reactivity data were used to classify VOCs into three reactivity classes: "negligibly reactive"; "reactive", and "highly reactive".

A kinetic study of the thermal decomposition of NH4NO3 in the presence of NaCl has been carried out using the differential kinetic technique previously described. The rate law for N2 evolution is of the form k1(NH4+)+k2(NH4+) (Cl—)½. A radical mechanism is proposed in which the role of chloride is catalytic, being oxidized by NO2+ to Cl atoms which are reduced back by NH4+ and NH3. These hydrogen abstraction reactions leave NH3+ and NH2, respectively, in reaction cages in which subsequent radical recombinations yield nitramide and nitrosamine as precursors for N2O and N2. Parallel Cl atom recombinations give Cl2, part of which escapes by volatilization, the rest reacting with NH3 to provide a second source of N2.

Photochemical air pollution is known to be caused largely by automotive emissions such as hydrocarbons and oxygenated hydrocarbon derivatives. Unlike the hydrocarbons, the contribution of the oxygenates has been virtually unexplored, mainly because of lack of appropriate analytical methods. The objective of this study was to identify and estimate the levels of oxygenated hydrocarbon derivatives in exhaust from simple hydrocarbon fuels. This information is expected to yield ultimately estimates of the relative levels of various classes of oxygenates in exhaust from full-boiling-range gasolines. Identification and measurement of oxygenates in exhaust from the simplified fuels were accomplished using gas chromatography in conjunction with time-of-flight mass spectrometry. The analytical procedure involved concentration of the exhaust organics, followed by a two-stage chromatographic separation of the resultant mixture of oxygenates and hydrocarbons. Identified oxygenates in exhaust from nine test fuels included saturated and unsaturated aldehydes, ketones, and alcohols, as well as ethers, esters, and nitroalkanes; analytical data on organic acids were inconclusive. Of the identified noncarbonyl oxygenates, phenols, cyclic ethers and nitromethane appear to be relatively the most abundant.